Sandbox defeats without fighting

Enjoying the sandbox battles so far, although a couple of times now I've suffered a defeat when I'm only an hour into a three hour battle (in "Hunt Them Down" mode), before troops have even engaged. In one defeat, I had already captured one of the objectives. In any event, given that I still have two more hours to find and defeat the enemy, it seems odd that games would end this early.

Can anyone explain what is happening and how to avoid these kind of defeats in future?

Impossible to answer that without knowing which scenario it is and what you did. A replay file would help a lot.

The basic game counts only points and points are won through (mainly) killing, routing or capturing enemy. The base game's scenarios also add points for objectives held but the KS mod scenarios do not accrue any points to either side for objectives; they are simply devices to focus the action at certain places on the battlefield in order to support the storyline of the scenario being fought.

And as you may realise, a "bodycount" does not give you a victory - tactical or grand tactical position is far more significant.

The result screen counts only points, and in our MP games these are seen as almost wholly irrelevant - we look at the final tactical position and determine winners/losers from that, and its here that holding objectives is much more important.

TL;DR - you can completely ignore the games result screen, decide if you won by watching the replay and seeing if you held the objective(s) you were ordered to.

hmmm, OK. Any way to just turn off the "Victory Announcements" completely, or jigger things so that they are not triggered?

We need to know why the scenario is ending early. Which scenario is it? Can you give a broad description of what is happening in the battle? It may be something easily fixable in the scenario.ini file.

Actually this has happened in Sandbox games, not scenarios.  

In all cases, I had either taken one objective (of two objectives) without encountering the enemy or was marching towards the first objective (also without encountering the enemy) when I received a pop-up message saying that I had suffered a defeat.  In all cases, there was at least an hour left in the battle.

It sounds like the scenario points limit has been reached by the AI side. If you assign objectives, try using the values in the attached screenshot. You can set more than one objective but the AI will always only attack or defend one of them, so for the player to win he/she should control both objectives at the end of the battle.

I set the objective time limit to 0 meaning it can't ever actually be captured, though the AI will still try to, and if you set the battle victory points total at bottom left extremely high, battles should not end early.

Great, thanks, will try that.